Effect of heated surface inclination on the growth dynamics and detachment of a vapor bubble, a numerical study
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ORIGINAL
Effect of heated surface inclination on the growth dynamics and detachment of a vapor bubble, a numerical study Ali Asghar Abdoli Tondro 1 & Reza Maddahian 2 & Ali Arefmanesh 3 Received: 3 December 2019 / Accepted: 31 July 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Nucleate boiling is an important part of the pool boiling phenomenon which occurs in various processes involving heat transfer, such as, steam production, chemical processes, etc. The inclination of the heated surface, where bubbles nucleates, significantly affects the bubble growth dynamics as well as the heat transfer rate from the microlayer underneath the bubble during the nucleate boiling. In this study, the effect of the surface inclination on the bubble growth and detachment during the nucleate boiling is investigated numerically. For this purpose, the proposed model of Lay and Dhir for the microlayer is modified to include the effect of the inclination of the heated surface. The resulting equations are solved numerically, and the effect of varying the inclination of the heated surface on the bubble growth and heat transfer is investigated. The results show that the largest bubble size and the highest heat transfer from the heated surface occur when the inclination of the heated surface is 30°; while, the smallest bubble size and the lowest heat transfer from the heated surface are observed for the horizontal surface. Furthermore, the total heat transfer from the inclined surface during the bubble growth increases up to 32% compared to that for the horizontal surface. Keywords Microlayer . Inclined heated surface . Nucleate boiling . Contact angle . Heat transfer
Nomenclature A Hamaker constant J. а1 Evaporation coefficient -. g Acceleration of gravity m/s2. h Latent heat kJ/ kg. K Interface curvature 1/m. k Thermal conductivity W/m.K. M Molecular weight g/mol. ˙ m Liquid mass flow rate kg/s. P Microlayer pressure Pa. * Ali Arefmanesh [email protected] Ali Asghar Abdoli Tondro [email protected] Reza Maddahian [email protected] 1
Thermal Power Plant Holding Co., Tehran, Iran
2
Faculty of Mechanical Engineering, Tarbiat Modares University, Tehran, Iran
3
Faculty of Mechanical Engineering, University of Kashan, Kashan, Iran
q ˙ Q R r e R T u
Microlayer conduction heat flux W/m2. Microlayer heat transfer rate W. Microlayer length mm. Distance from bubble base center mm. Universal gas constant J/mol. K. Temperature K. Liquid velocity m/s.
Greek Letters α Surface inclination -. β Contact angle -. δ Microlayer thickness mm. θ Tangential direction -. μ Viscosity kg /(m·s). ρ Density kg/m3. σ Surface tension N/m. Subscripts c Capillary. con Conduction. d Disjoining. g Gravity. i Inner. int Liquid-vapor interface. l Liquid.
Heat Mass Transfer
o 0 r sat sub sup v w z
Outer. horizontal surface Radial direction. Saturation. Subcooled. Superheat. Vapor. Wall. Axial direction.
1 Introduction Boiling phenomenon occurs in a variety of industrial apparatus. Steam generating boilers, chemical
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